TFTs have been currently widely applied in flat panel display devices due to good switching characteristic. In general, the TFT includes a gate electrode, an active area, a source electrode and a drain electrode. The source electrode and the drain electrode are respectively disposed at both ends of the active area and respectively make contact with the active area. For instance, when the voltage of the gate electrode is higher than the threshold voltage thereof, the source electrode and the drain electrode are conducted through the active area, and carriers flow from the source electrode to the drain electrode or from the drain electrode to the source electrode.
The active area of the TFT may be made of zinc oxynitride (ZnON) material. Compared with indium gallium zinc oxide (IGZO), when the ZnON material becomes electrical conductive, nitrogen vacancies (NVs) therein have high mobility, so that the conductivity of the TFT can be greatly improved. In addition, as the price of the ZnON material is cheaper than that of the IGZO material, the adoption of the ZnON material to form the active area can greatly reduce the manufacturing cost of the TFT.
However, different nitrogen contents in the ZnON material of the active area will result in different mobility. Moreover, in the electrical conduction process of the TFT and the annealing process of indium tin oxide (ITO) of a display substrate (e.g., an array substrate) of a display device, nitrogen in the active area will migrate to an adjacent gate insulating layer or an adjacent passivation layer due to the diffusion effect, so that the mobility of the NVs in the active area can be reduced, and hence the sub-threshold amplitude of the TFT can be increased. Moreover, the increase of the sub-threshold amplitude will severely affect the semiconductor characteristic of the TFT.